JP2006110423A - Treatment method of fly ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of fly ash, in which elution amount of heavy metals contained in fly ash generated when incinerating, melting or firing waste or fuel and adding sodium hydrogen carbonate (NaHCO<SB>3</SB>) into a flue in order to treat acidic gas is reduced by adding a small amount of chemicals, and the fly ash or the like is made harmless to an extent allowing landfill. <P>SOLUTION: In this fly ash treatment method, a chemical containing one or more kinds of substances selected from phosphoric acid, phosphate and ferrous salt is added to and mixed with fly ash, gas treatment residue or mixed ash thereof generated from an exhaust gas treatment facility for treating acidic gas by adding sodium hydrogen carbonate to the flue. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for treating fly ash. More specifically, the present invention relates to fly ash generated when incineration, melting, or calcination of waste, fuel, or the like, and sodium bicarbonate (sodium bicarbonate, NaHCO ₃ ) is added to the flue to treat acid gas. It is related with the processing method of fly ash which can reduce the elution amount of heavy metals contained in etc. by addition of a small amount of chemical | medical agents, and can make fly ash etc. harmless before a landfill disposal is possible.

When waste, fuel, etc. are incinerated, melted or calcined, the exhaust gas generated contains acidic gases such as chlorine and sulfur, so slaked lime (Ca (OH) ₂ ) has been added to the flue. Thus, a method for treating acid gas has been performed. Exhaust gas generated from incinerators contains harmful substances such as Pb, Cd, Hg, Cr (VI), As, and Se in addition to acid gases, and concentrates in fly ash, gas treatment residue, or mixed ash of these. Contained. As, Se and Cr (VI) are difficult to elute due to the effect of calcium in slaked lime, so when slaked lime is used for the treatment of acid gas, Pb, Cd and Hg are targeted for fly ash and water. Detoxification of harmful substances is generally performed by adding and mixing chelating agents and phosphoric acid.

In recent years, sodium hydrogen carbonate has been used as a more effective acidic gas treating agent in place of slaked lime. For example, as a simple and low-cost SO _{3 component} removal device that can remove sulfuric acid mist with high efficiency even when the amount of SO _{3 in} the flue gas fluctuates without using a wet electrostatic precipitator, A device for supplying sodium hydrogen carbonate powder to the upstream side of the desulfurization device arranged in the flue and controlling the sodium hydrogen carbonate supply amount according to the SO ₃ quantity detected at a predetermined location has been proposed. (Patent Document 1).

  When sodium hydrogen carbonate is used for the treatment of the acid gas, since the calcium content is small, it is necessary to perform insolubilization treatment of As, Se, and Cr (VI) in addition to the conventional Pb, Cd, and Hg. In order to insolubilize cadmium and lead in solid waste over a wide pH range, dry solid residue consisting of fly ash or a mixture of fly ash and bottom ash, and a water-soluble phosphate source in the presence of a free lime source Has been proposed (Patent Document 2). The present applicant first processed ash containing lead, hexavalent chromium, arsenic and selenium easily, efficiently and safely without the need for pH adjustment with a processing agent having excellent handleability. As a method for reliably preventing elution of lead, hexavalent chromium, arsenic and selenium from the treated material, water, ferrous compound and orthophosphoric acid are added to the ash containing lead, hexavalent chromium, arsenic and selenium. And a method of adding and kneading by adding monosodium dihydrogen phosphate, disodium monohydrogen phosphate or condensed phosphoric acid (Patent Document 3). However, it has not been clear that applying this method is particularly effective when using sodium bicarbonate for exhaust gas treatment.

On the other hand, sodium hydrogen carbonate has a high reaction efficiency with exhaust gas, so the amount of unreacted alkali that becomes a hindrance when fixing heavy metals with phosphoric acid is very small compared to slaked lime, and phosphoric acid is necessary. There is an advantage that the amount may be small, and in the case of ash from which As, Se and Cr (VI) do not elute originally, the treatment with phosphoric acid alone is clearly easier than in the case of slaked lime. The present inventors, first, neutral fly ash with a large variation in heavy metal content, without adding a calcium hydroxide source, without causing an increase in pH and an increase in the amount of the processed product, As a method that can be easily and efficiently treated, a phosphate compound having a molar ratio of alkali metal to phosphoric acid of 1 to 4 is added to neutral fly ash to bring the pH to a range of 6 to 12 A method of adjusting was proposed (Patent Document 4). This method does not use an exhaust gas treatment agent, and is a treatment method for ash having a pH of 5 to 9. Phosphoric acid having an alkali content because the optimum pH for fixing heavy metals is about 9 to 10 It was suitable to use a salt and there was no advantage to using phosphoric acid which is strongly acidic. However, fly ash treated with sodium bicarbonate often becomes weakly alkaline with a pH of 8 to 12, and therefore it is possible to use phosphoric acid in addition to phosphate.
JP 2002-263442 A (2nd page) Japanese Examined Patent Publication No. 4-61710 (first and third pages) JP 10-128273 A (second page) JP 7-155725 A (2nd page)

The present invention is included in fly ash generated when incinerating, melting or firing waste, fuel, etc., and adding sodium bicarbonate (sodium bicarbonate, NaHCO ₃ ) to the flue to treat acid gas. It was made for the purpose of providing a treatment method for fly ash that can reduce the elution amount of heavy metals by adding a small amount of chemicals and make the fly ash harmless before landfilling is possible. is there.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have made phosphoric acid, phosphates, etc. against fly ash generated from an exhaust gas treatment facility where sodium hydrogen carbonate is added to the flue. It has been found that iron (II) salts or drugs combining these exhibit a specific heavy metal elution preventing effect, and the present invention has been completed based on this finding.
That is, the present invention provides phosphoric acid, phosphate, and iron for fly ash, gas treatment residue, or mixed ash generated from an exhaust gas treatment facility that treats acidic gas by adding sodium hydrogen carbonate to the flue. (II) A fly ash treatment method comprising adding and mixing a chemical containing at least one selected from salts.

  According to the fly ash treatment method of the present invention, phosphoric acid is used for fly ash, gas treatment residue, or mixed ash generated from an exhaust gas treatment facility in which sodium hydrogen carbonate is added to a flue to treat acid gas. By adding and mixing a chemical containing at least one selected from phosphate and iron (II) salt, it is possible to effectively prevent elution of heavy metals from fly ash by adding a small amount of chemical. Can do.

In the method for treating fly ash according to the present invention, fly ash generated from an exhaust gas treatment facility for treating acid gas by adding sodium hydrogen carbonate (sodium bicarbonate, NaHCO ₃ ) to the flue, gas treatment residue, or a mixture thereof A chemical containing at least one selected from phosphoric acid, phosphate and iron (II) salt is added to and mixed with ash.

In a combustion furnace that incinerates, melts or burns industrial waste, municipal waste, fuel, etc., acidic gases such as sulfur trioxide, sulfur dioxide, and hydrogen chloride derived from sulfur compounds and chlorine compounds contained in the burned material Will occur. These acid gases not only corrode the combustion furnace equipment, but also cause environmental pollution if discharged into the atmosphere as they are. Therefore, by adding a powdery basic substance to the flue of the incinerator, Neutralization has been done. Conventionally, slaked lime has been widely used as a basic substance, but in recent years, sodium hydrogen carbonate has come to be used as a more effective acidic gas treating agent. The method of the present invention is applied to the treatment of combustion furnace fly ash, gas treatment residue, or mixed ash thereof using sodium hydrogen carbonate as a basic substance. Fly ash is ash collected by bag filters, electrostatic precipitators, etc. in combustion furnaces, melting furnaces, etc., and gas treatment residues are gases such as HCl and SO _x and gases such as Ca (OH) ₂ and NaHCO _3. It is a reaction product of a treating agent. The gas treatment residue does not include dust (ash) derived from combustion products such as garbage.

Examples of phosphoric acid used in the method of the present invention include linear polyphosphoric acid such as orthophosphoric acid H ₃ PO ₄ , diphosphoric acid, triphosphoric acid, tetraphosphoric acid, cyclic phosphoric acid and linear polyphosphoric acid. Examples thereof include metaphosphoric acid which is a mixture. Examples of the phosphate used in the method of the present invention include ammonium dihydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, barium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus Examples thereof include sodium ammonium oxyhydrogen, disodium hydrogen phosphate, dipotassium hydrogen phosphate, trisodium phosphate, tripotassium phosphate, sodium polyphosphate, potassium polarene, sodium metaphosphate, and potassium metaphosphate. Examples of the iron (II) salt used in the method of the present invention include iron fluoride (II), iron chloride (II), iron bromide (II), iron iodide (II), iron (II) sulfate, and thiocyanic acid. Examples thereof include iron (II), iron (II) phosphate, and iron (II) gluconate. In the method of the present invention, phosphoric acid, phosphate and iron (II) salt can be used singly or in combination of two or more.

  In the method of the present invention, the amount of the chemical containing at least one selected from phosphoric acid, phosphate and iron (II) salt to fly ash, gas treatment residue or mixture thereof is not particularly limited, but fly ash, etc. The amount of the drug is preferably 0.1 to 20 parts by weight, and more preferably 0.5 to 15 parts by weight. The component content of fly ash generated from combustion furnaces, gas treatment residues, or mixtures of these varies greatly depending on the combusted material, so elution is performed according to Environment Agency Notification No. 13 in advance for fly ash to be treated. It is preferable to conduct a test to determine an appropriate amount of drug to be added.

  In the method of the present invention, there is no particular limitation on the method of adding and mixing the chemicals to the fly ash, gas treatment residue or a mixture thereof. Water can be added and kneaded. FIG. 1 is an explanatory diagram of one embodiment of the method of the present invention. In this embodiment, raw ash composed of fly ash, gas treatment residue or a mixture thereof is charged into the hopper 1, and the chemical and water are added and kneaded in the barrel of the twin-screw kneader 2. By adding a small amount of water and kneading using a twin-screw kneader, the ash and the drug can be mixed uniformly, and the treatment effect by the drug can be sufficiently enhanced. In the embodiment shown in FIG. 1, the treated ash mixed with the drug by the twin-screw kneader is sent to the granulator 3 and is extruded and granulated at a high pressure. By granulating the treated ash, the volume can be reduced, the number of trucks for carrying out the treated ash can be reduced, and the final disposal site can be extended.

  Addition of a chelating agent to fly ash, gas treatment residue, or mixed ash generated from an exhaust gas treatment facility that treats acid gas by adding slaked lime to the flue effectively insolubilizes heavy metals. In addition, the elution concentration can be reduced. However, if a chelating agent is added to fly ash, gas treatment residue or mixed ash generated from an exhaust gas treatment facility that treats acid gas by adding sodium bicarbonate to the flue instead of slaked lime, heavy metals In order to insolubilize and lower the elution concentration, it is necessary to add a large amount of chelating agent. According to the method of the present invention, phosphoric acid, phosphate and iron (II) are added to fly ash, gas treatment residue or mixed ash generated from an exhaust gas treatment facility for treating acid gas by adding sodium hydrogen carbonate to the flue. By adding and mixing a drug containing one or more selected from the above, heavy metals can be efficiently insolubilized with a small amount of drug, and the elution concentration can be lowered.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the ash heavy metal dissolution test was conducted according to Environmental Agency Notification No. 13.
Table 1 shows the component contents of the mixed ash A, B, C and D of fly ash and gas treatment residue used in the examples and comparative examples. Ash A is the ash processed by adding sodium hydrogen carbonate to the flue of the industrial waste incinerator, and Ash B is the ash processed by adding sodium hydrogen carbonate to the flue of the municipal waste incinerator Ash C is an ash processed by adding slaked lime to the flue of an industrial waste incinerator, and ash D is an ash processed by adding slaked lime to the flue of a municipal waste incinerator.

Comparative Example 1
The sodium bicarbonate-treated ash A was subjected to a dissolution test. It was pH 11.0, Pb 3.5 mg / L, Cd less than 0.3 mg / L, Hg 0.052 mg / L, Cr (VI) 5.0 mg / L, As 0.92 mg / L and Se 0.4 mg / L.
Comparative Example 2
To 100 parts by weight of sodium bicarbonate-treated ash A, 20 parts by weight of water and 5 parts by weight of a chelating agent [Kurita Kogyo Co., Ltd., Ashnite S803] were added and kneaded in a mortar for 10 minutes, and then an elution test was performed. Pb was 3.2 mg / L, Cr (VI) was 5.0 mg / L, As was 0.91 mg / L, and Se was 0.4 mg / L.
Comparative Example 3
The same operation as in Comparative Example 2 was performed except that the addition amount of the chelating agent was 10 parts by weight. Pb was 0.32 mg / L, Cr (VI) was 4.8 mg / L, As was 0.92 mg / L, and Se was 0.4 mg / L.
Example 1
A 5: 5 mixture of 20 parts by weight of water and 75% by weight phosphoric acid (H ₃ PO ₄ ) aqueous solution and 30% by weight iron (II) chloride (FeCl ₂ ) aqueous solution in 100 parts by weight of sodium bicarbonate-treated ash A After adding 9.5 parts by weight and kneading in a mortar for 10 minutes, an elution test was performed. pH 10.5, Pb less than 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, and Se 0.3 mg / L. It was.
Example 2
The same operation as in Example 1 was performed except that the addition amount of the mixed solution of the phosphoric acid aqueous solution and the iron (II) chloride aqueous solution was 19 parts by weight. pH 10.2, Pb less than 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L there were.
The results of Comparative Examples 1-3 and Examples 1-2 are shown in Table 2.

As can be seen in Table 2, in Comparative Examples 2 to 3 in which a chelating agent was added to the sodium hydrogen carbonate treated ash A and kneaded, the elution concentrations of Cr (VI), As and Se were the same as those in Comparative Example 1. In Examples 1 and 2 in which phosphoric acid and iron (II) chloride were added and kneaded, the elution concentration of all heavy metals was below the landfill standard value, although it hardly decreased as compared with the treated ash.
Comparative Example 4
The dissolution test was performed on the sodium bicarbonate-treated ash B. pH 11.8, Pb 1.1 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L. It was.
Example 3
20 parts by weight of water and 1.3 parts by weight of a 75% by weight aqueous solution of phosphoric acid (H ₃ PO ₄ ) were added to 100 parts by weight of sodium bicarbonate-treated ash B, kneaded in a mortar for 10 minutes, and then subjected to an elution test. pH 11.0, Pb less than 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L there were.
Example 4
20 parts by weight of water and 1 part by weight of disodium hydrogen phosphate (Na ₂ HPO ₄ ) were added to 100 parts by weight of sodium bicarbonate-treated ash B and kneaded in a mortar for 10 minutes, and then an elution test was performed. pH 11.5, Pb 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L. It was.
Example 5
The same operation as in Example 4 was performed except that the amount of disodium hydrogen phosphate added was 2 parts by weight. pH11.3, Pb less than 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L there were.
Comparative Example 5
20 parts by weight of water and 1 part by weight of a chelating agent [Kurita Kogyo Co., Ltd., Ashnite S803] were added to 100 parts by weight of sodium bicarbonate-treated ash B, and after kneading in a mortar for 10 minutes, an elution test was performed. Pb was 1.0 mg / L.
Comparative Example 6
The same operation as Comparative Example 5 was performed except that the amount of the chelating agent added was 2 parts by weight. Pb was 0.4 mg / L.
Comparative Example 7
The same operation as Comparative Example 5 was performed except that the addition amount of the chelating agent was 3 parts by weight. Pb was less than 0.3 mg / L.
The results of Examples 3 to 4 and Comparative Examples 4 to 7 are shown in Table 3.

As can be seen in Table 3, in Examples 3 to 5 in which phosphoric acid or disodium hydrogen phosphate was added to the sodium bicarbonate-treated ash B and kneaded, phosphoric acid was 1 weight per 100 parts by weight of the ash. Pb elution concentration is less than 0.3 mg / L, and disodium hydrogen phosphate is 1 part by weight with respect to 100 parts by weight of ash, and Pb is just 0.3 mg / L of the landfill standard value. Addition of 2 parts by weight with respect to parts by weight results in a Pb of less than 0.3 mg / L. In Comparative Examples 5 to 7 in which a chelating agent was added to and kneaded with sodium hydrogen carbonate-treated ash B, the amount of the chelating agent was not increased to 3 parts by weight with respect to 100 parts by weight of ash, and less than Pb 0.3 mg / L Not.
Comparative Example 8
About the slaked lime processing ash C, the elution test was done. The pH was 12.5, Pb 100 mg / L, Cd less than 0.3 mg / L, Hg 0.03 mg / L, Cr (VI) 2.0 mg / L, As less than 0.3 mg / L, and Se less than 0.3 mg / L.
Comparative Example 9
To 100 parts by weight of slaked lime-treated ash C, 20 parts by weight of water and 5 parts by weight of a chelating agent [Kurita Kogyo Co., Ltd., Ashnite S803] were added and kneaded in a mortar for 10 minutes, and then an elution test was performed. Pb was 40 mg / L and Cr (VI) was 1.8 mg / L.
Comparative Example 10
The same operation as Comparative Example 9 was performed except that the addition amount of the chelating agent was 10 parts by weight. The Cr (VI) was 1.8 mg / L.
Comparative Example 11
9. A 5: 5 mixture of 20 parts by weight of water and 75% by weight aqueous solution of phosphoric acid (H ₃ PO ₄ ) and 30% by weight aqueous solution of iron (II) chloride (FeCl ₂ ) in 100 parts by weight of slaked lime ash C After adding 5 parts by weight and kneading in a mortar for 10 minutes, an elution test was conducted. Pb was 22 mg / L and Hg was 0.009 mg / L.
Comparative Example 12
The same operation as in Comparative Example 11 was performed except that the addition amount of the mixed solution of the phosphoric acid aqueous solution and the iron (II) chloride aqueous solution was 19 parts by weight. Pb was less than 0.3 mg / L and Hg was less than 0.005 mg / L.
The results of Comparative Examples 8 to 12 are shown in Table 4.

As seen in Table 4, in Comparative Examples 9 to 10 in which a chelating agent was added to the slaked lime-treated ash C and kneaded, the elution concentration of Cr (VI) did not decrease to the landfill reference value of 1.5 mg / L. . In Comparative Examples 11 to 12 in which phosphoric acid and iron (II) chloride were added and kneaded, the elution concentration of Pb and Hg was high when the addition amount with respect to 100 parts by weight of ash was 5 parts by weight, and the addition amount was 10 parts by weight. For the first time, the elution concentration of all heavy metals satisfies the landfill standard value.
Comparative Example 13
About the slaked lime processing ash D, the elution test was done. The pH was 12.6, Pb 27 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, and Se less than 0.3 mg / L.
Comparative Example 14
20 parts by weight of water and 4 parts by weight of a 75% by weight aqueous solution of phosphoric acid (H ₃ PO ₄ ) were added to 100 parts by weight of slaked lime-treated ash D, and after kneading in a mortar for 10 minutes, an elution test was conducted. Pb was 3.1 mg / L.
Comparative Example 15
The same operation as in Comparative Example 14 was performed except that the addition amount of the 75 wt% phosphoric acid aqueous solution was changed to 6.7 parts by weight. Pb was 0.34 mg / L.
Comparative Example 16
20 parts by weight of water and 2 parts by weight of a chelating agent [Kurita Kogyo Co., Ltd., Ashnite S803] were added to 100 parts by weight of slaked lime-treated ash D, and after kneading in a mortar for 10 minutes, an elution test was performed. pH 12.6, Pb less than 0.3 mg / L, Cd less than 0.3 mg / L, Hg less than 0.005 mg / L, Cr (VI) less than 0.2 mg / L, As less than 0.3 mg / L, Se less than 0.3 mg / L there were.
The results of Comparative Examples 13 to 16 are shown in Table 5.

  As seen in Table 5, in Comparative Examples 14 to 15 in which phosphoric acid was added to the slaked lime-treated ash D and kneaded, the addition amount of phosphoric acid was 5 parts by weight with respect to 100 parts by weight of ash. The elution concentration decreases only to 0.34 mg / L. On the other hand, in Comparative Example 16 in which 2 parts by weight of the chelating agent was added to 100 parts by weight of ash, the elution concentration of all heavy metals satisfied the landfill standard value.

  As can be seen from Table 1, the component content of the sodium bicarbonate-treated ash B and the slaked lime-treated ash D are substantially the same. However, as seen in Example 3 of Table 3, by adding 1 part by weight of phosphoric acid to 100 parts by weight of sodium bicarbonate-treated ash B, the elution concentration of all heavy metals satisfies the landfill standard value. On the other hand, as seen in Comparative Example 15 in Table 5, even when 5 parts by weight of phosphoric acid is added to 100 parts by weight of slaked lime-treated ash D, the landfill reference value for the elution concentration of Pb is not satisfied. From this result, it can be seen that phosphoric acid exhibits a heavy metal elution preventing effect specifically for ash generated from an exhaust gas treatment facility that treats acidic gas by adding sodium bicarbonate to the flue.

  As seen in Comparative Example 16 in Table 5, by adding 2 parts by weight of chelating agent to 100 parts by weight of slaked lime-treated ash D, the elution concentration of all heavy metals satisfies the landfill standard value, As seen in Comparative Examples 6 to 7 in Table 3, with sodium bicarbonate-treated ash B, 2 parts by weight of chelating agent is insufficient with respect to 100 parts by weight of ash, and the elution concentration of all heavy metals is the landfill standard value. In order to satisfy the above, it is necessary to add 3 parts by weight of a chelating agent. This result also shows that there is a difference in the effect of the heavy metal elution prevention treatment between the sodium hydrogen carbonate treated ash and the slaked lime treated ash.

  According to the fly ash treatment method of the present invention, phosphoric acid is used for fly ash, gas treatment residue, or mixed ash generated from an exhaust gas treatment facility in which sodium hydrogen carbonate is added to a flue to treat acid gas. By adding and mixing a chemical containing at least one selected from phosphate and iron (II) salt, it is possible to effectively prevent elution of heavy metals from fly ash by adding a small amount of chemical. Can do.

It is explanatory drawing of 1 aspect of implementation of the method of this invention.

Explanation of symbols

1 Hopper 2 Twin-screw kneader 3 Granulator

Claims (1)

  Select from phosphoric acid, phosphate and iron (II) salt for fly ash, gas treatment residue or mixed ash generated from an exhaust gas treatment facility that treats acid gas by adding sodium bicarbonate to the flue A method for treating fly ash, comprising adding and mixing a chemical containing at least one selected from the above.

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